1. Field of the Invention
This invention relates to a process for making a corrugated elastomeric tube which has an interior surface generally free from nipples, whereby the tube may be produced in a cost efficient manner.
2. Description of the Related Art
Corrugated elastomeric tubing has many applications, most of them involving a fluid which flows through the tubing. One possible application of the tubing is as a fuel line in automobiles. Presently, one type of process used for producing corrugated tubing causes nipples to be formed on the interior of the tubing. These nipples often break off when a fluid flows through the tubing, thereby potentially clogging a fuel filter, a carburetor or a fuel injector.
One such process having the potential for forming nipples on the interior surface of the tubing is described in British Pat. No. 1,167,146 which was published Oct. 15, 1969. This patent describes a method for manufacturing a corrugated tubing wherein the tubing is placed on a mandrel having an internal space or cavity. The tubing is sealed onto the mandrel at both ends. The exterior surface of the mandrel includes a plurality of convolutions. The gaps between the convolutions are in open communication with the cavity of the mandrel by way of ports. In operation, the tubing, while supported on the mandrel, is vulcanized or cured in an autoclave which forces the rubber of the tubing about the convolutions on the mandrel. The air trapped between the rubber tubing and the mandrel is forced into the cavity during the vulcanizing process so that the rubber lies flat against the mandrel as it is vulcanized. The rubber, being soft during the vulcanizing process, can flow into the holes in the mandrel and form nipples inside the tubing. In addition, sink holes can form in the exterior surface of the tubing over the mandrel holes. These same problems also may occur in processes wherein a vacuum is drawn on the interior of the mandrel.
Other processes known in the prior art utilize beads which wrap around the exterior surface of the elastomeric tubing in a helical manner to rigidly secure the underlying tubing to the mandrel. One such process is disclosed in U.S. Pat. No. 2,936,812, issued May 17, 1960 to Roberts. Corrugations in the tubing are formed by forcing air into an interior hollow space of the mandrel. This air then communicates with the exterior surface of the mandrel by means of mandrel ports. The air pressure forces the tubing between the beads to extend away from the mandrel, thus forming convolutions in the tubing because other parts of the tubing are secured to the mandrel by the beads. Production of many sections of the tubing using such a process can be somewhat expensive.
Other processes for producing such corrugated tubing sections are also known. A third such process is a process like that disclosed in U.S. Pat. No. 2,248,898, issued Jul. 8, 1941 to Ross et al. The process utilizes two mold halves which are clamped together. An elastomeric material is inserted within the mold halves, and air pressure is also supplied to the interior of the mold halves. The air pressure causes the elastomeric material to form a corrugated tube which conforms to the corrugated shape of the mold halves. Once again, it is generally expensive to produce tubing according to this process.
Thus, there is a need for a process of producing corrugated tubing which has a smooth interior surface free from nipples. Furthermore, it would be desirable to produce such an improved corrugated tubing in a cost efficient manner.